A fundamental challenge in the solar energy industry is to efficiently absorb and convert solar radiation into usable forms of energy. To this end, a variety of modern photovoltaic solar collecting (“PV”) systems exist. For example, some PV systems are static (“fixed panel arrays”); that is, their solar, or PV, solar collecting panels are fixed in a single plane and—often in the Northern Hemisphere—oriented in a southerly direction to maximize the incidence of solar radiation upon their panels. In general, static systems are far from optimized because they do not follow the sun and therefore do not capture the maximum solar power. Further, even where static PV panels are installed at the best possible solar angle, on average, they only produce 40-60% of the power that they are capable of producing.
Thus, in an effort to improve upon the efficiency of static solar systems, PV systems have been developed to track the motion of the sun (“tracking systems”). Solar tracking systems may track the sun about one or two axes. Tracking systems that move about a single axis are known as single axis tracking systems. Likewise, tracking systems that move about two axes are known as dual axis tracking systems.
Single axis tracking systems typically follow the motion of the sun from East to West; and this motion is commonly referred to as “azimuthal” tracking. Single axis tracking systems may yield an approximate 15-25% increase over the efficiency of a comparable static system (i.e., a system having a same number of collection elements). In like manner, dual axis tracking systems also follow the azimuthal motion of the sun and in addition, dual axis tracking systems follow the “zenithal” or seasonal motion of the sun. Zenithal motion represents the elevation of the sun above the horizon. For example, during the wintertime at Northern latitudes, the sun moves towards the South and is “lower” in the sky than it is during the summertime. Dual axis tracking systems yield approximately 40% or more power production over a fixed panel array.
Many dual axis tracking systems today comprise large racks of panels in an array mounted on a central vertical pole or post. In these systems, the number of panels that may be mounted is limited by the size and strength of the central pole and the foundation to support it. That is, the pole and mounting system must be sufficient to support the weight of the panel arrays mounted thereto and be constructed to withstand large wind loads. Pole mounted systems are self limiting because as one attempts to construct a larger pole mounted tracking array frame, one is required to continuously reinforce the pole and mounting system, and to increase the size of the supporting foundation. The costs associated with increased structural and foundation support are not cost-effective and are difficult to justify over the life span of the system.
What is needed, therefore, is a low cost and physically robust dual axis solar tracking array frame. In this regard, there have been several attempts to incorporate a dual axis tracking mechanism in a low cost framework. These primarily comprise a support frame structure with a rod and slide mechanism that uses linear actuators to move the solar panels into alignment on both axes.
For example, Thorley et al., U.S. Published Patent Application No. 2009/0250095 (“Thorley”) discloses a low-profile dual axis solar tracking module mounted on a circular frame and having multiple parallel rows of PV panels (FIGS. 16-26; para. [0090]).
The system described by Thorley suffers from various design flaws. For instance, referring to FIG. 16-26, it is apparent that each array of PV panels sits encompassed by a mounting frame or railing (e.g., see FIG. 19, circular frame 122; FIG. 26, rectangular frame 136). This frame or railing may cast one or more shadows on the PV array, particularly where the sun is at an oblique angle to the array (e.g., in the hours just after sunup and just before sundown). Additionally, the Thorley system is not easily scalable. Referring again to FIGS. 16-26, the frame itself, frame support or railing (e.g., FIG. 19, circular frame 122; FIG. 25, 26, frame support for primary axis 152) surrounding the PV array would at least inhibit the coupling of a second (and third and fourth, etc.) PV array thereto.
Thus, the systems and methods described in greater detail below solve the problems described above, including those described with reference to Thorley. Specifically, the systems and methods described herein comprise a low cost frame system, itself comprising a counterbalanced outer frame whose main members are connected and supported by crossbeams positioned underneath the main rails, and a plurality of counterbalanced internal frames or panel supporting structures seated at least partially within the perimeter of the outer frame. In this way, the stress and strain on pole mounted systems inherent in prior art systems are reduced, and less expensive frame materials are made available. Additionally, because the panels can be rotated to a vertical position either on command or when high winds are detected via sensors, wind loading is drastically reduced compared to pole mounted arrays. Further, by repositioning the end pieces that bound or enclose the outer frame to a location underneath the main rails of the outer frame, systems may be connected together and so are scalable. Moreover, this repositioning of frame materials allows one or more PV arrays to be coupled together and controlled by a single actuator or set of actuators. This feature may be assisted by the relative ease of motion resulting from counterbalancing the main and inner frames. Additionally, repositioning the end pieces underneath the main rails also positions them underneath the PV panels and so eliminates shading of the panels on each end. Further still, by mounting PV panels far apart, shading by one panel of another is reduced or eliminated.